Rapamycin assay

ABSTRACT

Monoclonal antibodies to rapamycin and to 40-O-alkylated derivatives of rapamycin are provided, together with novel haptens, immunogenic conjugates, and processes for making them and assay kits for using them.

This is a continuation of application Ser. No. 09/072,278, May 4, 1998,abandoned, which is a continuation of application Ser. No. 08/532,837,Oct. 5, 1995, abandoned, which is a 371 of PCT/EP94/01006, Mar. 30,1994.

This invention relates to monoclonal antibodies to rapamycin andrapamycin derivatives, which are useful, e.g., in assay kits formonitoring blood levels of drug.

Rapamycin is a macrolide antibiotic produced by Streptomyceshygroscopicus, which has been found to be pharmaceutically useful in avariety of applications, particularly as an immunosuppressant, e.g., foruse in the treatment and prevention of organ transplant rejection andautoimmune diseases. Rapamycin, however, does exhibit side effects athigher dosages, and it has a somewhat variable bioavailability.Monitoring blood levels of rapamycin in patients being treated withrapamycin is thus very desirable in order to be able to regulate thedosage so as to maintain the minimum level sufficient for pharmacologicactivity and to avoid any undue risk of side effects. The lack of asensitive and reliable assay which can be performed quickly and easilyin a clinical setting has been a major obstacle to the development ofrapamycin as a pharmaceutical.

Previous efforts to develop assay kits for clinical monitoring ofrapamycin have not been particularly successful. EP 041795, for example,describes a microbiological assay in which rapamycin concentration ismeasured as a function of antifungal activity. WO 92/02946 provides anassay system which measures rapamycin levels indirectly by measuringcompetition for binding to macrophilin. Both of these assays arecumbersome and not particularly sensitive. Even more importantly, bothof these assays may have considerable variation under slightly differenttest conditions, making comparisons of test results from differenthospitals difficult.

There have been no previous reports of monoclonal antibodies whichrecognize rapamycin. There are inherent difficulties in makingmonoclonal antibodies to rapamycin because rapamycin is not immunogenicand is itself extremely immunosuppressive. Moreover, as the metabolitesof rapamycin have not been well characterized in the literature, it isdifficult to identify a monoclonal antibody capable of differentiatingbetween rapamycin and its metabolites.

The present invention provides monoclonal antibodies which are highlysensitive to rapamycin. The antibodies of the invention are produced inresponse to inoculation with a novel immunogenic conjugate comprising anovel derivative of rapamycin linked to an immunogenic protein. Assaykits using these antibodies are well suited for use in a clinicalsetting and provide far more accurate and reproducible results than waspreviously possible. The antibodies are also useful in the purificationand isolation of rapamycin.

Providing assay systems for immunosuppressive derivatives of rapamycinpresent similar challenges. Of particular interest are 40-O-derivativesof rapamycin, i.e., rapamycins which are O-substituted at the hydroxy onthe cyclohexyl ring (position 40), e.g., as described in U.S. Pat. No.5,258,389 and PCT/EP 93/02604 (O-aryl and O-alkyl rapamycins) (bothincorporated herein by reference); especially 40-O-alkylated rapamycinswhere the 40-O-substituent is alkyl or substituted alkyl; e.g.,hydroxyalkyl, hydroxyalkoxyalkyl, acylaminoalkyl, or aminoalkyl, wherein“alk-” or “alkyl” refers to C₁₋₆ alkyl, branched or linear, preferablyC₁₋₃ alkyl, in which the carbon chain may be optionally interrupted byan ether (—O—) linkage; most especially 40-O-(2-hydroxyethyl)-rapamycin,40-O-(3-hydroxypropyl)-rapamycin,40-O-[2-(2-hydroxy)ethoxy]ethyl-rapamycin, and40-O-(2-acetaminoethyl)-rapamycin). Thus a further object of theinvention is to provide monoclonal antibodies to such 40-O-derivatives.Such antibodies are useful in diagnostic assays and also in thepurification and production of the derivatives.

The novel activated derivatives of rapamycin used to make the novelimmunogenic conjugates of the invention are rapamycins which are linkedthrough one of the hydroxy groups on the rapamycin, preferably thehydroxy group located on the cyclohexyl portion of the rapamycin(position 40) or the hydroxy at position 28, to an activated couplinggroup, i.e., a group capable of direct reaction with a protein to form acovalent linkage without the requirement for the use of a coupling agent(e.g., carbodiimide reagents) to enable, effect, or promote the reactionwith the protein. Preferably, the activated coupling group has anactivated ester or carboxy group, i.e., of formula —CO—O—X where X is acarboxy activating group such as o- or p-nitrophenyl, 1-benztriazole,pentafluorophenyl, or (especially) N-succinimido. Other suitableactivated coupling groups are, for example, i) activated dithio groups,e.g., of formula —S—S—Z wherein Z is a dithio activating group such as2-pyridyl, which may be linked to the rapamycin; or ii) epoxy groups,e.g., epoxy methyl. The activated coupling group may be linked to therapamycin by means of an ester, ether, amide, thio or other suitablelinkage, but ester linkage is preferred. Most preferably, the activatedcoupling group contains a bis-ester moiety, e.g., succinyl, having anester linkage to the rapamycin at one end and the activated ester oractivated carboxy group at the other.

The preferred rapamycin derivatives of the invention are those offormula III below which are produced according to Reaction I:

wherein formula I is rapamycin, which is a) reacted with an acylatingagent, e.g., a cyclic anhydride or a dicarboxylic acid (optionally inhemi-O-protected form), under suitable conditions and deprotection ifnecessary to yield the rapamycin of formula II, wherein Y is a spacermoiety, preferably a lower alkylene, e.g., C₂₋₆ alkylene, mostpreferably ethylene. This rapamycin of formula II is then b) activatedby reaction with a carboxy activating group, e.g. of formula HO—X whereX is as defined above, to yield the activated rapamycin of formula III.

A preferred activated derivative of rapamycin is the succinimidoderivative of formula III below, prepared, e.g., according to ReactionII:

wherein formula I is rapamycin, which is a) 0-acylated using succinicanhydride in the presence of DMAP and pyridine to form the rapamycinhemisuccinate of formula II′ (40-O-(3-Carboxy)propanoyl-rapamycin);which is then b) activated with N-Hydroxy succinimide in the presence ofEDC, Et₃N, and CH₂Cl₂ to form the 40-O-succinimidooxysuccinyl rapamycinof formula III′, e.g., as described more fully in example 1 below.Monoclonal antibodies produced using a hapten such as this which islinked through the 40-position will ordinarily be cross reactive betweenrapamycin and a 40-O-derivative of rapamycin, such as described above.Such monoclonal antibodies can be selected as described below forcompounds which recognize a particular region of the rapamycin or40-O-derivative of the rapamycin, e.g., in the binder domain or effectordomain, as described below.

It is in some cases desirable to have monoclonal antibodies capable offine sensitivity to modifications in the cyclohexyl region, e.g., fordistinguishing between rapamycin and the 40-O rapamycin derivatives, orfor identifying metabolites in the cyclohexyl region. In such a case,the hapten is preferably linked through the 28-O position rather thenthe 40-O position. For example, the rapamycin derivative of formula A:

wherein R is an O-protecting group, or a substituent as described above,e.g., hydroxyalkyl, hydroxyalkoxyalkyl, acylaminoalkyl, or aminoalkyl,optionally in protected form, is reacted according to Reaction I,deprotecting if necessary, to give the analogous 28-O activated hapten,for example a compound of formula B:

wherein R1 is H, or an O-substituent as described above, e.g.,hydroxyalkyl, hydroxyalkoxyalkyl, acylaminoalkyl, or aminoalkyl, Y is alinker moiety as defined above, and X is a carboxy activating group asdefined above. In preparing this hapten, where R is an O-protectinggroup or an O-protected substituent, the acylating agent may optionallybe, e.g., a dicarboxylic acid in hemi-O-protected form, so thatfollowing acylation, both O-protecting groups may be removed in one stepprior to adding the carboxy activating group. For example, haptens forgenerating monoclonal antibodies capable of recognizing40-O-(2-hydroxyethyl)-rapamycin, can be produced by protecting theprimary hydroxy, acylating the hydroxy at position 28 with adicarboxylic acid in hemi-O-protected form, deprotecting, and activatingthe carboxy group, e.g., according to Reaction III:

Similarly, rapamycin itself may be activated at the 28-O rather than the40-O, by O-protecting the C40 hydroxy, acylating the hydroxy group inposition 28 with a hemi-O-protected dicarboxylic acid, deprotecting, andactivating the carboxy group, e.g., according reaction IV:

The activated rapamycin or rapamycin derivative is then linked to asuitable immunogenic protein, e.g., bovine serum albumin (BSA),ovalbumin (OVA), or keyhole limpet hemocyanine (KLH) to form animmunogenic conjugate. Monoclonal antibodies are prepared usingconventional methods, e.g., administering the novel immunogenicconjugate to a suitable animal species to effect immunogenic challengeand recovering antibody-producing cells sensitized to said conjugate;immortalizing said antibody producing cells by fusion with a suitablemyeloma; and recovering the monoclonal antibody from a selectedimmortalized cell line thus established.

The antibodies of the invention may then be used in a suitable assay.Several possibilities would be clear to one skilled in the art. Oneapproach is a competitive assay using antibody and a rapamycin tracer,for example wherein microtiter plates are coated with antibody andexposed to a competitor which is a labeled (e.g., fluoro- orradio-labeled, especially biotinylated) rapamycin, in the presence andabsence of test fluid believed to possibly contain a rapamycin, e.g.,plasma or whole blood from the patient. The plates are rinsed, and theamount of labeled competitor which has bound to the antibody ismeasured, which amount varies inversely with the amount of rapamycin inthe test fluid. Another approach is an ELISA using antibody, a rapamycinprotein conjugate, and a labeled (e.g., enzyme-labeled) tracer antibodyrecognizing murine IgG, for example wherein microtiter plates are coatedwith a rapamycin-protein conjugate (e.g., the immunogenic conjugatedescribed above comprising a protein linked to rapamycin or a40-O-alkylated rapamycin), exposed to antibody in the presence andabsence of test fluid, rinsed, and antibody binding to the rapamycinconjugate detected by binding of the tracer antibody to the antibodybound to the rapamycin conjugate. Again, the amount of bound antibodywill vary inversely with the amount of rapamycin in the test sample. Ineither case, the assay is standardized with test solutions containingknown concentrations of rapamycin. An assay kit comprising (i) themonoclonal antibody of the invention, preferably in lyophilized form orcoated onto a microtiter plate, and (ii) optionally also comprisingeither a rapamycin protein conjugate, optionally coated onto a plate,and/or a labeled rapamycin derivative, and (iii) further optionallycomprising a rapamycin solution for standardization and instructions foruse, is therefore provided. Such a kit is capable of detecting rapamycinat concentrations of below 10 ng/ml, e.g., below 1 ng/ml, e.g., as lowas 0.25-0.5 ng/ml.

The antibodies of the invention may be further characterized by theirrelative binding affinity to an immunosuppressive ascomycin, e.g.,FK-506. FK-506 is an immunosuppressive macrolide having some structuralsimilarity to rapamycin in the binding domain. Rapamycins (e.g.,rapamycin and its immunosuppressant derivatives) and FK-506 both bind tomacrophilins (FKBPs), and for both it is believed that macrophilinbinding is a necessary but not a sufficient criteria forimmunosuppressive activity. The effector region of rapamycin, however,is quite different from FK-506, and indeed, the two compounds have quitedifferent mechanisms of activity. (FK-506 for example appears to causeimmunosuppression primarily by suppressing IL-2 transcription, whereasrapamycin has no significant effect on IL-2 transcription.) Rapamycinscan thus be characterized as having an FKBP binding domain and aneffector domain, and a distinction can be made between rapamycinmetabolites which are modified in the FKBP binding domain from thosemodified in the effector domain. This distinction can be made with themonoclonal antibodies of the invention by measuring the relativecross-reactivity of the monoclonal antibodies of the invention withFK-506 (cross-reactivity being measured, e.g., in a competitive ELISA):monoclonal antibodies having a high degree of cross reactivity (e.g.,greater than 50%) recognize epitopes in the FKBP binding domain ofrapamycin which is similar to FK-506; monoclonal antibodies with a lowdegree of cross reactivity (e.g., less than 20%, optimally less than10%) recognize epitopes in the effector region, which is unique torapamycins.

Antibodies of the invention can also be screened and characterizedaccording to their ability to distinguish between rapamycin and a40-O-derivative of rapamycin, e.g., as defined above. Where it isdesired that the antibodies do not distinguish between rapamycin and a40-O-derivative of rapamycin, antibodies are selected which show atleast 70%, preferably greater than 90%, cross-reactivity betweenrapamycin and a 40-O-derivative thereof. In such a case, the hapten usedto make the monoclonal antibody is preferably a 40-O-activatedrapamycin, e.g., of formula III in Reaction I. Where it is desired todistinguish between rapamycin and a 40-O-derivative or metabolite ofrapamycin, antibodies are selected having less than 30%, preferably lessthan 10%, cross-reactivity thereto. In this case, the hapten used tomake the antibody is preferably a 28-O-activated rapamycin or rapamycinderivative, e.g., of formula B.

EXAMPLE 1 Production of 40-O-activated Rapamycin

a) Production of 40-O-hemisuccinate of Rapamycin

To a stirred solution of 1.5 g (1.64 mmol) of rapamycin and 0.577 g(5.77 mmol) of succinic anhydride in 12 mL of pyridine is added 195 mg(1.64 mmol) of DMAP. The resulting mixture is stirred at ambienttemperature for 19 h and concentrated under reduced pressure. Theresidue is dissolved in ethyl acetate and washed three times with water.The organic solution is dried over anhydrous sodium sulfate, filteredand concentrated under reduced pressure. The residue is purified bycolumn chromatography on silica gel using 9:1 CH₂Cl₂—MeOH. The fractionscontaining the expected product are combined and purified once more bycolumn chromatography on silica gel using 19:1 CH₂Cl₂—MeOH to afford,after removal of the solvent under reduced pressure,40-O-(3-carboxy)propanoyl-rapamycin (the rapamycin hemisuccinate offormula II′ supra) as a white foam showing the following characteristicspectroscopic properties:

¹H NMR (CDCl₃) δ2.68 (7H, m, H33, H25 and O₂CCH ₂CH ₂CO₂H), 3.14 (3H, sand m, OCH₃ and H39), 3.34 (3H, s, OCH₃), 3.38 (3H, s, OCH₃), 4.68 (1H,m, H40), 4.72 (1H, broad s, 10-OH); MS (FAB) m/z 1036 ([M+Na]⁺), 982([M-CH₃O]⁺), 964 ([M-(CH₃O+H₂O)]⁺), 946 ([M-(CH₃O+2H₂O)]⁺).

b) Production of 40-O-succinimidooxysuccinyl-rapamycin

To a stirred solution of 120 mg (0.118 mmol) of the rapamycinhemisuccinate of step a), 16.5 μL (0.118 mmol) of Et₃N and 22.7 mg(0.118 mmol) of EDC in 8 mL of CH₂Cl₂ is added 13.6 mg (0.118 mmol) ofN-hydroxysuccinimide. The resulting mixture is stirred for 18 h at roomtemperature, then diluted with ethyl acetate and washed twice withwater. The organic solution is dried over anhydrous sodium sulfate,filtered and concentrated under reduced pressure. The residue ispurified by column chromatography on silica gel (ethyl acetate) toafford 40-O-succinimidooxysuccinyl-rapamycin (i.e., the compound offormula III′ in Reaction II supra) as a white foam having the followingcharacteristic spectroscopic properties:

¹H NMR (DMSO) δ2.67 (2H, t, O₂CCH ₂CH₂CO₂), 2.81 (7H, s, CH₃O andsuccimide CH₂), 2.92 (2H, t, O₂CC₂CH ₂CO₂), 4.55 (1H, m, H40), 5.26 (1H,d, 28-OH), 6.43 (1H, s, 10-OH); MS (FAB) m/z 1133 ([M+Na]⁺), 1111([M+H]⁺), 1092 ([M-H₂O]⁺), 1079 ([M-CH₃O]⁺), 1061 ([M-(CH₃O+H₂O)]⁺),1043 ([M-(CH₃O+2H₂O)]⁺).

EXAMPLE 2 Production of 28-O-activated 40-O Derivative of Rapamycin

a) 28-O-hemisuccinate of 40-O-(2-hydroxyethyl)-rapamycin

To a stirred, cooled (0° C.) solution of 958 mg (1.00 mmol) of40-O-(2-hydroxyethyl)-rapamycin in 2.2 mL of 10:1 methylenechloride-pyridine is added 0.160 mL (1.50 mmol) of allyl chloroformate.Stirring is continued at 0° C. and two portions each of 0.080 mL (1.00mmol) of pyridine and 0.053 mL (0.50 mmol) of allyl chloroformate areadded after 3 hours and 4 hours respectively. After the last addition ofreagents, stirring was continued for one more hour, and the reaction isquenched with 1M aqueous sodium bicarbonate. The resulting mixture isextracted three times with ethyl acetate. The organic solution is washedsuccessively with 1N aqueous hydrochloric acid, 1N aqueous sodiumbicarbonate and saturated brine, then dried over anhydrous sodiumsulfate, filtered and concentrated under reduced pressure. The residueis purified by column chromatography on silica gel (50:50 hexane-ethylacetate) to afford the allyloxycarbonyl protected compound (formula 2 inreaction III above) as a white foam.

To a stirred, cooled (0° C.) solution of 208 mg (0.200 mmol) of thisproduct in 2 mL of methylene chloride is added 2.4 mg (0.020 mmol) ofDMAP and 82 mg (0.400 mmol) of DCC, followed by a solution of 63 mg(0.400 mmol) of monoallylsuccinate in 0.5 mL of methylene chloride. Thereaction mixture is stirred at 0° C. for 14 hours and the resultingsuspension was filtered through a fritted glass funnel. The organicsolution is concentrated under reduced pressure, and the residue ispurified by column chromatography on silica gel (30:70 hexane-ethylacetate) giving the product (formula 3 of reaction III above) as a whitefoam.

To a stirred solution of 177 mg (0.150 mmol) of this product in 5 mL ofmethylene chloride is added 17.3 mg (0.015 mmol) oftetrakis(triphenylphosphine)palladium and 0.080 mL (0.3 mmol) oftributyltin hydride. The yellow solution is stirred for 2 hours atambient temperature and diluted with ethyl acetate, washed once withcold 2N aqueous citric acid and three times with saturated brine, driedover anhydrous sodium sulfate, filtered and concentrated under reducedpressure. Column chromatography on silica gel (85:15 ethylacetate-methanol) affords the hemisuccinate (formula 4 of reaction III)as a pale yellow oil.

b) 28-O-succinimidooxysuccinyl-40-O-(2-hydroxyethyl)-rapamycin

A solution of 53 mg (0.050 mmol) of the hemisuccinate of step a) in 2.5mL of methylene chloride is treated with 2 mg of DMAP, 24 mg (0.125mmol) of EDC and 14 mg (0.125 mmol) of N-hydroxysuccinimide. Afterstirring for 2 hours at ambient temperature, the reaction is quenchedwith 1N aqueous sodium bicarbonate. The mixture is extracted with threeportions of ethyl acetate. The organic solution is washed with aqueoussodium bicarbonate and brine, dried over anhydrous sodium bicarbonate,filtered and concentrated to give the title activated hapten (thecompound of formula 5 of reaction III), which is used for thepreparation of the protein-hapten conjugate without furtherpurification, and which has the following characteristic spectrascopicproperties:

¹H NMR (CDCl₃) δ2.43 (1H, dd, H33a), 2.50-2.98 (10H, m, H25, H33b,succinate hydrogens, succinimide hydrogens), 3.58 (2H, m, H6b, 1hydroxyethyl H), 3.68 (3H, m, H16, 2 hydroxyethyl H), 3.81 (2H, m, H14,1 hydroxyethyl H), 3.93 (1H, d, H27), 5.28 (2H, m, H2, H30), 5.34 (1H,d, H28); MS (FAB) 1161 ([M+Li]⁺).

EXAMPLE 3 Production of 28-O-activated Rapamycin

a) 28-O Hemisuccinate of Rapamycin

To a stirred, cooled (0° C.) solution of 914 mg (1.00 mmol) of rapamycinin 2.2 mL of 10:1 methylene chloride-pyridine is added 0.212 mL (2.00mmol) of allyl chloroformate. After 3 hours 0.080 mL (1.000 mmol) ofpyridine and 0.053 mL (0.50 mmol) of allyl chloroformate are added.Stirring is continued for one more hour, and the reaction is quenchedwith 1M aqueous sodium bicarbonate. The resulting mixture is extractedthree times with methyl-t-butylether. The organic solution is washedsuccessively with cold 1N aqueous hydrochloric acid, 1N aqueous sodiumbicarbonate and saturated brine, then dried over anhydrous sodiumsulfate, filtered and concentrated under reduced pressure. The residueis purified by column chromatography on silica gel (70:30 hexane-ethylacetate) to afford the allyloxycarbonyl protected compound (formula 2 inreaction IV) as a white foam.

To a stirred, cooled (0° C.) solution of 400 mg (0.400 mmol) of thisproduct in 5 mL of methylene chloride is added 4.8 mg (0.040 mmol) ofDMAP and 164 mg (0.800 mmol) of DCC, followed by a solution of 127 mg(0.800 mmol) of monoallylsuccinate in 1 mL of methylene chloride. Thereaction mixture is stirred at −15° C. for 14 hours and the resultingsuspension is filtered through a fritted glass funnel. The organicsolution is concentrated under reduced pressure and the residue ispurified by column chromatography on silica gel (40:60hexane-methyl-t-butylether) giving the compound of formula 3 of ReactionIV as a white foam.

To a stirred solution of 285 mg (0.250 mmol) of this product in 5 mL ofmethylene chloride is added 28.8 mg (0.025 mmol) oftetrakis(triphenylphosphine)palladium and 0.133 mL (0.5 mmol) oftributyltin hydride. The yellow solution is stirred for 1 hour atambient temperature and diluted with methyl-t-butylether, washed twicewith cold 2N aqueous citric acid and three times with saturated brine,dried over anhydrous sodium sulfate, filtered and concentrated underreduced pressure. Column chromatography on silica gel (90:10-60:40methyl-t-butylether-methanol) affords the 28-O rapamycin hemisuccinate(the compound of formula 4, reaction IV) as a pale yellow oil.

b) 28-O-succinimidooxysuccinyl-rapamycin

A solution of 51 mg (0.050 mmol) of the product of step a) in 2 mL ofmethylene chloride is treated with 2 mg of DMAP, 24 mg (0.125 mmol) ofEDC and 14 mg (0.125 mmol) of N-hydroxysuccinimide. After stirring for 4hours at ambient temperature, the reaction is quenched with 1N aqueoussodium bicarbonate. The mixture is extracted with three portions ofmethyl-t-butylether. The organic solution is washed with aqueous sodiumbicarbonate and brine, dried over anhydrous sodium bicarbonate, filteredand concentrated to give the activated title compound, which is used forthe preparation of the protein-hapten conjugate without furtherpurification and which exhibits the following characteristicspectrascopic properties:

¹H NMR (CDCl₃) δ2.43 (1H, dd, H33a), 2.55-3.02 (11H, m, H25, H33b, H39,succinate hydrogens, succinimide hydrogens), 3.56 (1H, m, H6b), 3.68(1H, dd, H16), 3.83 (1H, m, H14), 3.93 (1H, d, H27), 5.28 (2H, m, H2,H30), 5.34 (1H, d, H28); MS (FAB) 1117 ([M+Li]⁺).

EXAMPLE 4 Production of Immunogenic Conjugates

a) 40-O-linked Rapamycin Conjugates

17.4 mg of the 40-O-activated rapamycin of example 1 is dissolved in 400μl DMF or DMSO. 120 μl (i.e., containing 5.22 mg activated rapamycin) ofthis solution is added dropwise with vigorous stirring to a solutioncontaining 8 mg of KLH in 2 ml 0.1 M NaHCO₃ buffer (pH 7.7). Thereaction mixture is stirred for 2 hours at room temperature, and theresulting rapamycin-KLH conjugate is purified by dialysis at 4° C.against 5 l PBS, 3× over 48 hours. The conjugate is optionally furtherconcentrated by centrifugation using microconcentrator tubes.Rapamycin-BSA and rapamycin-OVA conjugates are prepared in the samemanner, substituting BSA or OVA respectively for KLH in the aboveprocedure.

b) 28-O-linked (optionally 40-O-alkylated) Rapamycin Conjugates

5 mg of the 28-O-activated compound of example 2 is dissolved in 2 mlDMSO and added dropwise with vigorous stirring to a solution containing5 mg KLH in 1 ml 50 mM phosphate buffer (PH 7.3). The reaction mixtureis stirred for 2 hours at room temperature, and the resulting conjugateis purified by dialysis at 4° C. against 2 l PBS, 3× over 48 hours.Conjugates with BSA and OVA conjugates are prepared in the same manner.Rapamycin is conjugated to KLH, BSA, and OVA through position 28 usingthe 28-O activated compound of example 3, following the same procedure.

EXAMPLE 5 Production of Monoclonal Antibody

a) Monoclonal Antibody to Rapamycin

Monoclonal antibody is produced by using conventional techniques,essentially as described by Köhler and Milstein in Nature 256: 49.Female Balb/C mice (20-25 g) each receive 10 or 50 μg of the 40-O-linkedrapamycin-KLH immunogenic conjugate of example 4a) in 0.2 ml completeFreund adjuvant, administered by subcutaneous injection at four sites.After 2 weeks a second booster injection comprising the same amount ofthe immunogenic conjugate emulsified in 0.2 ml of incomplete Freundadjuvant is administered, again by s.c. injection. The presence ofantibodies reactive to the antigen in the animals' blood serum isconfirmed by direct ELISA as described in example 6 below. The mice mayoptionally be further selected for antibody to the effector region (lowcross reactivity with FK-506) and to the FKBP binding region (high crossreactivity to FK-506). FIG. 1, for example, shows titer curves for amouse (M1) having a high level of antibody to the binding domain ofrapamycin, and another mouse (M7) having relatively high levels ofantibody to the effector domain. Mice displaying maximal blood serumlevels of antibody of appropriate specificity receive booster injectionscomprising 10 μg of antigen half i.p. half i.v. on day −3, and i.p. onday −2 and −1. On day 0. the mice are sacrificed and their spleen cellsare isolated and fused with PAI-0 cells or other suitable myeloma line.The resulting hybridomae are cultured and selected using ELISA forexpression of antibody having a high affinity to rapamycin.

b) Monoclonal Antibody to 40-(hydroxyethyl)-rapamycin

Female Balb/C mice receive 10 or 50 μg of the40-(hydroxyethyl)-rapamycin KLH immunogenic conjugate of example 4b) in0.2 ml complete Freund's adjuvant by s.c. injections on 4 points. After2 weeks, a second injection (booster) comprising the same quantity ofimmunogenic conjugate emulsified in 0.2 ml incomplete Freund's adjuvantis administered, again by s.c. injection. The presence of antibodiesreactive to the antigen in the animal's blood serum is tested by directELISA as described below. In addition, mice are further selected forantibody to the region of the rapamycin molecule modified in the 40-Oregion by binding to a conjugate of BSA-rapamycin compared to aconjugate of BSA-40-O(2-hydroxyethyl)-rapamycin. Both antibodies whichbind to the 40-O(2-hydroxyethyl)-rapamycin conjugate but do not bind toconjugated rapamycin, and antibodies which bind both to40-O(2-hydroxyethyl)-rapamycin and rapamycin conjugates are obtained.Mice displaying maximal blood serum levels of antibody of appropriatespecificity receive booster injections comprising 10 μg of antigen halfi.p. half i.v. on day −3, and i.p. on day −2 and −1. On day 0. the miceare sacrificed and their spleen cells are isolated and fused with PAI-0cells. The resulting hybridoma are cultured and selected using ELISA forexpression of antibody having a high affinity to40-O-(2-hydroxyethyl)-rapamycin.

EXAMPLE 6 Enzyme Linked Immunosorbent Assay (ELISA)

a) ELISA for Rapamycin

Microtiter plates are coated with 1-2 μg/ml rapamycin-BSA conjugate inPBS for 2 hours at 37° C., then saturated with 2% BSA in PBS for 1 hourat 37° C., and washed 3× with 0.05% Tween-PBS. The hybridomasupernatants to be screened are diluted in a 1% solution of BSA in PBS,and incubated overnight at room temperature (or 18 hours at 4° C. or 2hours at 37° C.). Level of bound antibody is measured by anti-mouse IgGgoat globulin coupled to alkaline phosphatase withpara-nitrophenylphosphate as the substrate. After incubation for twohours at 37° C., the enzymatic substrate is hydrolysed (i hour at roomtemperature) and absorbance at 405 nm is measured. Hybridomae areselected for production of high affinity monoclonal antibody.

Standard curves to determine relative affinity of a selected antibody torapamycin are prepared using solutions containing known concentrationsof rapamycin (e.g., 1 to 140 ng/ml in blood serum). FIG. 2, for example,shows a standard curve for our monoclonal antibody M7-91, demonstratingthat that monoclonal antibody, which was selected as being highlyspecific for rapamycin, is capable of detecting rapamycin at levels aslow as 0.25 ng/ml.

Antibodies may be further characterized as binding to the effector orFKBP binding domains of rapamycin by measuring cross reactivity withFK-506 in an analogous direct ELISA using microtiter plates coated withFK506-BSA conjugate, which can be prepared analogously to rapamycin-BSAconjugate. For example, a comparison of binding levels of 17 selectedmonoclonal antibodies in the rapamycin-BSA and FK-506 assays is shown inFIG. 3; cross reactivity as a percentage is shown in FIG. 4. In thiscomparison of binding to rapamycin-BSA vs. FK506-BSA, monoclonalantibodies of very low affinity are detected.

The above direct ELISA may be converted to a competitive ELISA wherein acompetitor is added to the monoclonal antibody solution, and binding ofthe monoclonal antibody to the conjugate in the presence and absence ofthe competitor is measured. Where the competitor is FK506 or arapamycin, the competitor in ethanolic solution, e.g., 1 mg/ml isdirectly added to the monoclonal antibody solution (e.g., 2 μl/200μl/well) and further diluted in the microtiter plate. FIG. 5, forexample, shows an inhibition curve for binding of the M7-91 antibody(M7.91.13) to BSA-rapamycin in the presence of different concentrationsof free rapamycin. In such competitive ELISAs comparing the binding ofthe monoclonal antibodies to free FK506 vs. free rapamycin, less crossreactivity between rapamycin and FK506 is seen than in the direct ELISA.Such a competitive assay is preferred for selection of monoclonalantibodies, because it is believed that some monoclonal antibodies mayhave too low an affinity to bind their antigen in free form in solutionbut may nevertheless show bivalent or polyvalent binding to themultimeric antigen, which comprises many haptens bound in closeproximity to one another on a large protein molecule. A competitiveassay excludes such low affinity antibodies. The results of such acompetitive assay are shown in FIG. 6, which compares the M7-91 antibody(M7.91.13) which has relatively low cross reactivity with M1-303(M1.303.3) antibody which has relatively high cross reactivity.

b) ELISA for 40-O-(2-hydroxyethyl)-rapamycin

This ELISA is performed analogously to the procedure described in a).Microtiter plates are coated with 40-O-(2-hydroxyethyl)-rapamycin-BSA,saturated with BSA and washed. The hybridoma supernatants to be screenedare incubated 18 hours at 4° C. or 2 hours at 37° C. Level of boundantibody is measured by anti-mouse IgG goat globulin coupled to alkalinephosphatase with para-nitrophenylphosphate as the substrate. A parallelELISA is performed using bound rapamycin-BSA to select for monoclonalantibodies capable of distinguishing 40-O-(2-hydroxyethyl)-rapamycinfrom rapamycin. FIG. 7 shows, for example, supernatants of hybridomaB3-203 binding selectively to 40-O-(2-hydroxyethyl)-rapamycin-BSA(referred to in the figure as BSA-28-RAD) (FIG. 7A), of hybridoma B3-113recognizing both 40-O-(2-hydroxyethyl)-rapamycin-BSA and rapamycin-BSAconjugated through position 28 (FIG. 7B), and of hybridoma B3-164 thatrecognize in addition rapamycin coupled to BSA through position 40 (FIG.7C).

The relative affinity of the antibodies to40-O-(2-hydroxyethyl)-rapamycin versus rapamycin is further measured bycompeting the binding of the antibodies to the coated40-O-(2-hydroxyethyl)-rapamycin-BSA conjugate with40-O-(2-hydroxyethyl)-rapamycin or rapamycin free in solution. FIG. 8,for example, shows that antibodies produced by hybridoma B3-203 reactstrongly with 40-O-(2-hydroxyethyl)-rapamycin with low crossreactivityfor rapamycin (FIG. 8A) and that antibodies produced by hybridoma B3-113and B3-164 bind equally well to 40-O-(2-hydroxyethyl)-rapamycin andrapamycin (FIGS. 8B and 8C). Other hybridomae producing antibodiesbinding at least 10-100-fold better to 40-O-(2-hydroxyethyl)-rapamycinthan to rapamycin include B3-22, B3-127 and B3-156. Other hybridomaesuch as B3-29, B3-265 and B3-539 produce antibodies that bind rapamycinas well as 40-O-(2-hydroxyethyl)-rapamycin.

Once the desired antibody has been selected, the same ELISA is used todetermine blood levels of rapamycin in patients. An assay kit accordingto this example would provide one or more selected antibodies inlyophilized form, a microtiter plate coated with a rapamycin conjugate(e.g., rapamycin-BSA conjugate or 40-O-(2-hydroxyethyl)-rapamycin-BSAconjugate), a rapamycin standard, and instructions for use. Optionally,the kit may further comprise a labelled rapamycin derivative for use ina competitive assay. Anti-mouse IgG-enzyme conjugate and substrate asdescribed above may additionally be provided. Alternatively, thecustomer may use the monoclonal antibody of the invention in his ownestablished ELISA or other assay system.

What is claimed is:
 1. An immunogenic conjugate which is 1) rapamycinbearing an immunogenic protein at position 40 or 28; or 2)40-O-(2-hydroxyethyl)-rapamycin bearing an immunogenic protein atposition
 28. 2. An immunogenic conjugate of claim 1 which is produced byreacting an immunogenic protein with either 1) rapamycin bearing anactivated coupling group at position 40 or 28; or 2)40-O-(2-hydroxyethyl)-rapamycin bearing an activated coupling group atposition 28, wherein the activated coupling group is —CO—O—X where X isa carboxy activating group, —S—S—Z where Z is a dithio activating group,or an epoxy group.
 3. An immunogenic conjugate comprising a rapamycinportion and a protein portion wherein the rapamycin is i)40-O-succinimidooxysuccinyl-rapamycin, ii)28-O-succinimidooxysuccinyl-rapamycin, or iii)28-O-(succinimidooxysuccinyl)-40-O-(2-hydroxyethyl)-rapamycin.
 4. Animmunogenic conjugate which is produced by reacting a protein with arapamycin derivative bearing an activated coupling group wherein therapamycin is i) 40-O-succinimidooxysuccinyl-rapamycin, ii)28-O-succinimidooxysuccinyl-rapamycin, or iii)28-O-(succinimidooxysuccinyl)-40-O-(2-hydroxyethyl)-rapamycin.